The key difference between incandescence and iridescence is that incandescence occurs due to heat whereas iridescence occurs due to alteration of the angle of light.
Light is a type of electromagnetic radiation. It is visible to the naked eye of humans. The main source of light is the sun. However, there can be some other phenomena that can produce or alter the light. Incandescence and iridescence are two such phenomena.
What is Incandescence?
Incandescence is the process of producing light from a heated solid material. This light is in the visible electromagnetic radiation; therefore, we see it as a colour. In addition, other types of radiation also emit (thermal radiation) from a hot object, but this is not incandescence. In incandescence, light is produced as a result of the increased temperature. Therefore, it is a special type of thermal radiation.
The basic principle of incandescence is giving energy to atoms by heating. When a solid heats, it turns red first (at this point, the object emits enough radiation, so we can observe the colour). Red is the lowest energy colour in the visible range we can observe. Upon further heating, it becomes white. We see it as white because we are giving enough energy to the material so that the electrons in it are energized in many different ways, and the collection of those appears as white light.
For example, we can see incandescence when an iron bar is heated to a high temperature. Then the iron bar starts to glow in red and orange colour, which is visible to us. Here, some of the heat energy supplied to the iron bar has turned into light energy.
Incandescence is useful in incandescent light bulbs to produce light. These bulbs have a filament that can withstand very high temperatures without melting. The filament also has a long lifetime. When heating this filament, it emits radiation that falls into the visible region, producing light. However, most of the radiation is emitted in the infrared part in the spectrum; therefore, we feel the heat. This is why the efficiency of bulbs is less in producing light. If there is an element that can withstand very high temperature, the efficiency could be high. Sunlight is also due to the incandescence of the sun.
What is Iridescence?
Iridescence is an optical phenomenon where we see different colours as we change the angle of observing. If not, the differences can be observed if the angle of illumination changes. This is a property of certain surfaces. We can see surfaces like this in nature a lot. For example, butterfly wings, feathers of birds and shells of some animals, some parts of plants have this property. The cause for this is the change in the reflection of incidental radiation.
During this process, some wavelengths in the incidental light undergo amplification, and some attenuate. If the two light waves are in phase, they are amplified. If they are out of phase, destructive interference cancels them off. In multiple layer structures of animals, iridescence occurs. This is due to thin-film interference. For example, eyes of cats contain multilayer structures that improve night vision. Therefore, they produce iridescent metallic-like reflections.
What is the Difference Between Incandescence and Iridescence?
The key difference between incandescence and iridescence is that incandescence occurs due to heat whereas iridescence occurs due to alteration of the angle of light. Moreover, heat is an essential component in incandescence, but there is no need for heat energy in iridescence.
The following infographic summarizes the difference between incandescence and iridescence.
Summary – Incandescence vs Iridescence
Incandescence and iridescence are two processes that can produce light and alter the light respectively. The key difference between incandescence and iridescence is that incandescence occurs due to heat whereas iridescence occurs due to alteration of the angle of light.
1. Craig Freudenrich. “How Light Works.” HowStuffWorks Science, HowStuffWorks, 27 Jan. 2020, Available here.
2. “Incandescence.” Wikipedia, Wikimedia Foundation, 23 Feb. 2020, Available here.
3. “Iridescence.” Wikipedia, Wikimedia Foundation, 16 Mar. 2020, Available here.
1. “Hot metalwork” By fir0002flagstaffotos [at] gmail.comCanon 20D + Tamron 28-75mm f/2.8 – Own work (GFDL 1.2) via Commons Wikimedia
2. “Soap Bubble – foliage background – iridescent colours – Traquair 040801” (CC BY-SA 3.0) via Commons Wikimedia